Anyone running a 55, 56, 57 truck rear end? Why not?

[4SFEDZ]

What's the deal with the stock rear ends? Anyone running one? Are they just weak? I have a 56 3200 factory v8 truck. I'm looking to put a 350 (maybe 300 hp) in it and od tranny. Could I still run stock rear?

[capnduane]

Excellent question, has been on my mind a long time. I have the stock rear end in my '55 2nd and have a Pontiac 400 with probably 325 hp in it. I drive it conservativly and don't smoke the tires.

[meter swinger]

I think most are swapped out for gear ratio and bolt pattern changes. I changed mine out for one out of 78 k10 with 308 gears.

[OrrieG]

Relatively strong, in the old days hot trick was to use a truck 8 lug for drag racing for strength and gear ratio. Meter swinger hit it, if you change the front to 5 lug then you are caring 2 spares and they were geared for 45 mph farm roads and in the city delivering stuff.

[Henry50]

I have one in my 50 with a pretty strong 350 and th350.

From what I have read there pretty strong.
I haven't been real hard on it but I have gotten on it a few times and smoked the tires.

[roger55]

Parts are very limited for them. I think there are only 2 ratios available and those are off-shore made. No posi units.

http://www.tomsdifferentials.com/201...og/Pages13.pdf

[mr48chev]

The main thing is that they just flat don't have the gear ratio that the vast majority of guys building Task Force trucks want for running down the highway at highway speeds. A couple of vendors have ring and pinions that can be swapped with better ratios but in the end that usually runs the tab up to several hundred dollars and you are still stuck with six lug drums.

Back in the mid 70's I had a 57 Panel with a 327 that ran Jahns 12.5 pistons, Engle solid lifter cam and 2.02 heads with a 2x4 early Corvette intake and carbs and then a Holley 750 on a 300 hp 327 intake. Stock three speed and stock rear axle. It would stay with a 750 Honda in a two block street race and pull the front wheels if you wanted to. It also got 3 mpg on the highway running 70. The rear end stood up to the abuse but the clutch didn't as I blew a clutch racing a Mercedes a block from my work in Waco on my lunch hour and I was pulling him when the clutch went. No complaints about the strength of that rear end though.

I put a complete drive train out of a 56 into my friends 53 including 235, 3 speed and 56 rear axle and he and his wife did a 10 K road trip in it with custom camper on the back right afterwards. It also has the best paint job I ever did on it that has held up well for 30 years. That truck had the low powered engine and hauled a pretty good load though.

I even have a 55 axle going under my roadster because I am running 18 inch 32 Chevy wires on it that are six lug. The fact that it was free didn't hurt either and it going behind a 254 Ford flathead six with a compound four speed behind it. I won't drive it long distances too often so highway speed isn't a huge issue.

The main issue is still road speed and gas mileage on the road along with wheel choice and running more modern and bigger brakes.

[capnduane]

My '55 pulls about 3grand at 60mph with the stock 3.90 gears and 28in tires. Gas mileage is about 12 on a good day! A T5 tranny would be great, but you would need one with a high ratio first gear. My Muncie 4 speed has a 2.20 or 2.54 first.

[Old Truck Man]

I always wanted to run mag wheels. So back in the day I would use 54 car hubs drums ect to change over the front axle to 5 lug. So next was to change the rear end. Simply weld the spring perches to whatever 5 lug rear end I had available. With a stick trans I preferred a 355 gear ratio.

[_Ogre]

Originally Posted by 4SFEDZ

Could I still run stock rear?

yes, stock is fine

unless you want to run highway speeds
stock rearends are high ratio (i thought 4.11), open spool aka one-wheel-wonders
thus i changed to a 3.27 posi rearend w/700r4 overdrive trans and i get 20mpg running 80mph

[mr48chev]

Originally Posted by _Ogre

yes, stock is fine

unless you want to run highway speeds
stock rearends are high ratio (i thought 4.11), open spool aka one-wheel-wonders
thus i changed to a 3.27 posi rearend w/700r4 overdrive trans and i get 20mpg running 80mph

If wheel choice and having a trick suspension isn't an issue that is the whole key right there. Engine rpm at highway speed. Add to that actually being able to drive at highways speeds for serious lengths of time without overly stressing the engine or using far more gas than you might.

When I put the 283 in my 48 in 1975 with a M21 Muncie and a Nova rear end of unknown gear ratio along with N-50 14 tires on the back my tach read 3K at 80 mph. As Capnduane said his truck with 3.90 gears pulls 3K at 60 mph. Not that one needs to get somewhere that much faster but for those of us who routinely make road trips in our trucks of several hundred or even thousand miles that is a lot of engine wear and extra gas burned. If all you intend to do is drive it around town on Saturdays or Sundays for a couple of hours and a "long" road trip is to a show 50 miles away from the house once a year it isn't quite as important.

[roger55]

The 3.38 gear would work pretty well with a TH350 or 700R4. Thing is do you want to buy off-shore gears for $300+. Of course if the rear needs anything else, then it becomes apparent that it's better to put the money towards another type of rear where USA parts and posi units are available.

[1project2many]

I'm running 225/75 16 tires. Engine speed with original trans and most common 3.90 rear gear is 2686 at 60 mph, 3133 @ 70 mph. With NVG4500 trans and OD, highway RPM would be 1961 and 2287. Fuel mileage with stock trans is between 16 and 18 mpg. Engine is efi equipped 302 with small chamber 305 heads and old 325 hp 327 camshaft.

Pinion seal was replaced when truck put on road back in 92 or so. LH axle seal started to leak while towing way too heavy trailer across country in December of '98. Old truck axle has shield and drain so leaking oil won't contaminate brakes! Find that on a new axle. Seal never replaced, leak stopped (gotta love old leather seals) and still in use today. Yes... I checked the oil level.

Lack of parts and lack of flexibility are the strongest negatives for this old axle. If you want six lug with numerically lower gear ratio and you've got a mild engine, switch to 8.5" gm truck or older truck 12 bolt.

[roger55]

My '57 pickup was switched to a '65 GMC pickup rear before I bought it. It's a Dana 44. I had it completely rebuilt with new 3.54 gears, trac-lock posi unit and all the bearings. The only problem I had was finding new brake drums for it. They don't have them anymore. I ended up getting Jeep Waggoneer drums for it. They fit perfect except for the center axle flange hole. I had a machine shop enlarge them for me. I also had to modify the brake backing plates to accept the stock e-brake cables.

[62lwbc10]

I'm running a brand GM crate motor (350/290) with a mildly worked and very fresh TH350 with the completely original rear end. With this setup I'm revving about 2600 RPM at 55 mph. Great for around town but not so much for extended highway rides. Motor is strong and more than adequate but it's not a monster either. I suspect with tall highway gears it would be a dog. With the original rear (must be at least 4.11) and the tricked out tranny, it's pretty torquey around town and chirps second easily at half throttle.

[4SFEDZ]

62lwbc10, how tall of a tire is that? A taller tire will drop your rpms. But with an overdrive tranny like a 700r4 it shouldn't be too bad tho right?

[gag1025]

was running that differential and then swapped it our for a later model Camaro differential because I wanted a higher gear ratio (I no longer care to drag). There is nothing wrong with the '55 Chevy differential that I can see. If anyone close by wants to buy it I will sell it for $100. It is ready to bolt up.

[Katrina/10]

I put the Yukon 3.38 gears in my 55, very happy with them. Good for highway use and around town.

[yossarian19]

I hear variously that the 55T rear end came in 3.90 or 4.10. In either case, you'll need to compensate with tire size and / or an overdrive trans to keep the RPM down for highway use.
You can't readily escape the drum brakes.
No traction devices available.
Parts are hard to find / expensive relative to a 12 bolt or a Dana axle.
6 lugs. To me, this is a "pro" because more lugs on a larger bolt circle = manlier.
Those are the "Cons"
Pros:
It's an 8.4 ring gear with threaded adjusters, dropout third member, standard / easy to find and cheap brake parts, stud mounted everything and a fabricated housing. If you want to use your truck like a half-ton, get some 30" or equivalent tires on there & forget about it. Want an off-road truck, 12 bolt or 14 bolt or Dana 60.
If you want to build a muscle car... well, start by purchasing a muscle car. If that doesn't work out, then sure, get a 10 bolt or a Dana 44 or a 12 bolt or whatever, because it's going to be a lot easier to work with.

[_Ogre]

Originally Posted by yossarian19

To me, this is a "pro" because more lugs on a larger bolt circle = manlier.